The World Wide Web (Web) is a network of information resources. The Web relies on three mechanisms to make these resources readily available to the widest possible audience: (1) A uniform naming scheme for locating resources on the Web (e.g., Uniform Resource Identifiers); (2) Protocols, for access to named resources over the Web (e.g., HTTP); and (3) Hypertext, for easy navigation among resources (e.g., HTML).
A Universal Resource Locator (URL) is a type of Uniform Resource Identifier (URI). Every resource available on the Web—an HTML document, an image, a video clip, a program, etc.—has an address that is encodable by a URL. URLs typically consist of three pieces: (1) The naming scheme of the mechanism, or protocol, used to access the resource; (2) The domain name of the machine hosting the resource; and (3) The name of the resource itself, given as a path.
For example, the following URL, “http://www.example.com/important.htm” indicates that the protocol to be used is HyperText Transfer Protocol (HTTP) and that the domain name of the resource is “www.example.com” and that the resource is named “important.htm.” That is, the URL locates a resource on the Web and, given the appropriate protocol, a program can retrieve that resource. As such, a URL alone provides a great deal of information. Service providers and enterprises can inspect URLs in order to obtain this information for purposes such as statistical purposes. Further, software programs or data communications devices can block traffic to undesired sites based on URLs.
The Domain Name System (DNS), also referred to as the Domain Name Service, is an Internet service that translates domain names into IP addresses. Domain names are alphanumeric and therefore are easier for people to remember. The Internet, however, is based on IP addresses. The format of an IP address is a 32-bit numeric address written as four numbers separated by periods. Each number can range from zero to 255. For example, 1.160.10.240 is a possible IP address. DNS translates every domain name transmitted from a Web browser into the corresponding IP address. For example, the domain name “www.example.com” might translate to 198.105.232.4. The DNS system is its own network. If one DNS server does not know how to translate a particular domain name, it asks another DNS server, and so on, until the correct IP address is returned.
When a browser on a client connected to the Web forms a connection to a Web server and requests a page, the browser first divides the Web page's URL into three parts: (1) the protocol (“http”); (2) the domain name (“www.example.com”); and (3) the file name (“important.htm”). The browser then communicates with DNS to translate the domain name “www.example.com” into an IP address which is used to connect to the server. The browser then forms a connection to the server at that IP address. Following the HTTP protocol, the browser sends a GET request to the server, asking for the file “http://www.example.com/important.htm”. The server sends the HTML text of the Web page to the browser in response to the GET request. The browser reads the HTML tags in the HTML text and formats the page for display.
Network Address Translation (NAT) is an Internet standard that enables a local area network (LAN) to use one set of IP addresses for internal traffic and a second set of addresses for external traffic. NAT serves three main purposes: (1) NAT provides a type of firewall by hiding internal IP addresses; (2) NAT enables an organization to use more internal IP addresses (since the IP addresses are used only internally, they do not conflict with IP addresses used by other companies and organizations); and (3) NAT allows a company to combine multiple ISDN connections into a single Internet connection.
A content delivery network (CDN) is a network of servers that delivers a Web page to a user based on the geographic locations of the user, the origin server of the Web page and local servers. Within the CDN, copies of the pages of a Web site are stored in local servers called content engines (also called edge servers) that are dispersed at geographically different locations, caching the contents of the Web page. Content routers in the CDN route user requests to an appropriate content engine. When a user requests a Web page that is part of a CDN, the CDN redirects the request from the originating site's server to a server in the CDN that is closest to the user and delivers the cached content from that closest server. The CDN also communicates with the originating server to deliver any content that has not been previously cached. This service is effective in speeding the delivery of content of Web sites with high traffic and Web sites that have global reach. Typically, the closer the content engine is to the user geographically, the faster the content will be delivered to the user. CDNs also provide protection from large surges in traffic.